The valve is a device used to control the direction, pressure and flow of the fluid in the fluid system, which can make the medium (liquid, gas, powder) in the piping and equipment flow or stop and control its flow. The valve is an important control component in the fluid delivery system.

Preparation before operation
Before operating the valve, carefully read the operating instructions. The flow direction of gas must be clear before operation, and the valve opening and closing signs should be checked. Check the appearance of the valve to see if the valve is affected with damp. If it is affected with damp, dry it; If other problems are found, they should be handled in a timely manner, and no operation with faults is allowed. If the electric valve is out of service for more than 3 months, check the clutch before starting, and then check the insulation, steering and electrical circuit of the motor after confirming that the handle is in the manual position.

Correct operation method of manual valve
Manual valve is the most widely used valve. Its handwheel or handle is designed according to ordinary manpower, taking into account the strength of the sealing surface and the necessary closing force. Therefore, do not use a long lever or a long wrench to move. Some people are used to using the wrench, so they should pay close attention to it. When opening the valve, they should use steady force to avoid using excessive force to open or close the valve. The force should be steady and not impact. Some parts of high pressure valves with impact opening and closing have considered that the impact force cannot be equal to that of ordinary valves.

When the valve is fully opened, the handwheel should be turned back a little to make the threads tight to avoid looseness and damage. For rising stem valves, remember the valve stem position when fully open and fully closed to avoid hitting the top dead center when fully open. It is convenient to check whether it is normal when it is fully closed. If the valve stem falls off, or large debris is embedded between the valve core seals, the valve stem position will change when it is fully closed. Damage of valve sealing surface or valve handwheel.

Valve opening sign: when the groove on the top surface of the valve stem of ball valve, butterfly valve and plug valve is parallel to the channel, it indicates that the valve is in the fully open position; When the valve stem rotates 90 to the left or right. When the groove is perpendicular to the channel, it indicates that the valve is in the fully closed position. Some ball valves, butterfly valves and plug valves are opened when the wrench is parallel to the channel, and closed when the wrench is vertical. The three-way and four-way valves shall be operated according to the marks of opening, closing and reversing. Remove the movable handle after operation.

Correct operation method of safety valve
The safety valve has undergone pressure test and constant pressure before installation. When the safety valve has been operating for a long time, the operator should pay attention to the inspection of the safety valve. During the inspection, people should avoid the outlet of the safety valve, check the lead seal of the safety valve, pull up the safety valve with a wrench by hand, and open it at intervals to remove dirt and verify the flexibility of the safety valve.

Correct operation method of steam trap
The drain valve is easy to be blocked by water dirt and other sundries. When it is enabled, first open the flushing valve and flush the pipeline. If there is a bypass pipe, the bypass valve can be opened for temporary flushing. For the drain valve without flushing pipe and bypass pipe, the drain valve can be removed. After opening the shut-off flushing valve, close the shut-off valve, install the drain valve, and then open the shut-off valve to enable the drain valve.

Correct operation of pressure reducing valve
Before starting the pressure reducing valve, open the bypass valve or flushing valve to clean the dirt in the pipeline. After the pipeline is flushed, close the bypass valve and flushing valve, and then start the pressure reducing valve. Some steam pressure reducing valves have steam traps in front of them, which need to be opened first, then slightly open the shut-off valve behind the pressure reducing valve, finally open the shut-off valve in front of the pressure reducing valve, watch the pressure gauges in front of and behind the pressure reducing valve, adjust the adjusting screw of the pressure reducing valve, so that the pressure behind the valve reaches the predetermined value, then slowly open the shut-off valve behind the pressure reducing valve, and correct the pressure behind the valve until it is satisfactory. Fix the adjusting screw and cover the protective cap.

If the pressure reducing valve fails or needs to be repaired, the bypass valve shall be opened slowly, and the shut-off valve in front of the valve shall be closed at the same time. The bypass valve shall be roughly adjusted manually to make the pressure behind the pressure reducing valve basically stable at the preset value, and then the pressure reducing valve shall be closed, replaced or repaired, and then returned to normal.

Correct operation of check valve
In order to avoid the high impact force formed at the moment when the check valve is closed, the valve must be closed quickly, so as to prevent the formation of a great reverse flow velocity, which is the cause of the impact pressure when the valve is suddenly closed. Therefore, the closing speed of the valve should be correctly matched with the attenuation speed of the downstream medium.

If the velocity variation range of the downstream medium is large, the minimum velocity is not enough to force the closure to stop stably. In this case, the movement of the closing element can be restrained by a damper within a certain range of its action stroke. The rapid vibration of the closing parts will cause the moving parts of the valve to wear too fast, leading to premature failure of the valve. If the medium is pulsating flow, the rapid vibration of the closing element is also caused by extreme medium disturbance. In this case, the check valve should be placed at the place with the minimum medium disturbance.